Indicating fuse



May 11, 1965 F. J. KOZACKA INDICATING FUSE Filed March 22, 1963 a 3 5 48 9 2 a. G. M M .1... H H m 6 7 M 3 4. 2 G a 5 M a 9 mfl f fi r, f"fldrm TC mm 0 WK an K m R E D E R F.

United States Patent 3,183,327 INDICATING FUSE Frederick J. Kozaclra,South Hampton, N.H., assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Mar. 22, 1963, Ser. No. 267,192 4 Claims. (Cl.200-121) This invention has reference to electric fuses.

It is one object of this invention to provide improved electric fuses ofthe so-called dual element type which fuses are provided with pin meansadapted to indicate blowing of the particular fuse, or to perform somemechanical operation, e.g. closing of a signalling contact, or trippingof a circuit breaker, in response to blowing of the particular fuse.

Dual element fuses comprise two distinct and separate circuitinterrupting means, of which one becomes operative upon occurrence ofmajor fault currents, or shortcircuit currrents, while the otherinterrupting means hecomes operative upon occurrence of relatively smalloverload currents of inadmissible duration. Interruption of a circuitupon occurrence of relatively small overload currents of inadmissibleduration can effectively be carried out by separation of a pair ofcooperating contacts.

It is, therefore, another object of this invention to provide dualelement the overload persists for too long a period of time and furtheradapted to indicate interruption of the circuit, irrespective of whetherthe interruption is caused by a major fault current, or short-circuitcurrent, or by a relatively small overload current of inadmissibleduration.

Another object of this invention is to provide dual element fuses havinga high interrupting capacity and in which so-called follow currents aresuppressed when the fuses blow as a result of a major fault current, orshortcircuit current.

For a better understanding of the invention reference may be had to theaccompanying drawings in which:

FIG. 1 is a vertical section along a dual element fuse embodying thepresent invention taken along 11 of FIG. 2;

FIG. 2 is a vertical section of the dual element fuse of FIG. 1 takenalong 22. of FIG. 1; and

FIG. 3 is a top-plan View of the fuse of FIGS. 1 and 2.

Referring now to the drawings, numeral 1 has been applied to indicate afusible element formed by a multiperforated fusible ribbon. Ribbon 1 ismade of a metal having a relatively high conductivi y and a relativelyhigh fusing point, preferably silver. Rectangular perforations 2 inribbon 1 result in formation of a plurality of serially related pointsof reduced cross-sectional area along ribbon 1. Ribbon 1 is embedded ina pulverulent arc-quenching substance 3, preferably quartz sand. Atubular casing 4 of insulating material as, for instance, a syntheticresin-fiber-glass-cloth laminate, houses ribbon 1 and the pulverulentarc-quenching substance 3. The length of ribbon 1 arranged within casing4 is less than that of casing 4. As a result, the upper end of casing 4projects beyond ribbon 1 at the upper end thereof. This provides atubular space 4:: inside of casing 4 not coextensive with, and notoccupied by, ribbon 1. Reference numeral 5 has been applied to indicatea housing or cylinder arranged inside of tubular casing 4 in coaxialrelation thereto. Housing 5 occupies the aforementioned tubular space 4aand accommodates a piston 6 and a compressed helical spring 7 biasingpiston 6 away from ribbon 1. Housing 5 segregates piston 6 and spring 7from the arc-quenching substance or filter 3 inside of casing 4. Pistonrod 8 is arranged below the lower surface of piston 7 and projectstransversely through housing 5 toward ribbon 1. Piston rod 8 is made ofmetal, e.g. brass, and has a sufficiently large cross-sectional area toimpart to it a larger current carrying capacity than ribbon 1. The lowerend of piston rod 8 is slotted at St: and the upper end of ribbon 1 isinserted into the slot formed by piston rod 8. Soft solder joint 9firmly secures the lower slotted end of piston rod 8 to the upper end offusible ribbon 1. Liquid solder applied to ribbon 1 adjacent the areathereof overlapped by piston rod 8 flows by capillary action into theslot 8a of the latter, thus tending to establish a firm bond betweenparts 1 and 8 which has a very small ohmic resistance. Indicator pin it)of electric insulating material is arranged on the upper side of piston6, or the side thereof remote from solder joint 9. Pin 10 may beprovided at its lower end with a screw-thread (not shown) allowing toscrew it into the upper surface of piston 6. Housing 5 forms an integralpart of a terminal cap 11 mounted on the upper surface of casing 4 andclosing the upper end of casing 4. To be more specific, terminal cap 11defines a recess coaxial with casing 4 and extending into casing 4 in adirection longitudinally thereof, and it is this recess which forms ahousing 5 accommodating piston 6, spring '7 and insulating pin itInsulating disc 12 is press-fitted into said recess and provided with acentral aperture 13 for the passage of pin 10. The lower end of casing 4is closed by a terminal cap 11a mounted on the outer surface of casing 4and provided with a slot 14 sage of the lower end of ribbon 1 from theinside of casing to the recess which is considerably shallower than therecess provided in cap 11 and the recess in cap 11a is filled with abody 15 of soft solder. This body of soft solder establishes aconductive connection between the lower end of ribbon 1 and terminal cap11a. The perforated end surface of lower terminal cap 11a issubstantially flush with the lower end of casing 4.

On occurrence of major fault currents, or short-circuit currents,fusible ribbon 1 fuses substantially Simultaneously at all its points ofreduced cross-sectional area defined by major fault current, orshort-circuit current, by fuses is known as follow current. Protractedsmall follow curents may result in fail are of a fuse subsequent to asuccessful interruption by it, of a major fault current, orshort-circuit current.

F danger is eliminated in fuses embodying this invention by virtue ofthe fact that spring 7 is free, upon fusion of the highest point ofreduced cross-section of ribbon 1 On occurrence of relatively smalloverload currents of moved into inadmissible duration the heat generatedat the points of reduced cross-sectional area of ribbon 1 is sufficientto soften solder joint 9. As a result, piston rod 8 and piston 6 arefree to move upwardly under the action of spring 7. This establishtes acircuit interrupting gap between ribbon l and piston rod 8. At the sametime insulating pin it) is propelled by spring '7beyond casing 4i, thusclearly indicating that the overloaded circuit is interrupted.

As long as the fuse is intact the current path through it is as follows:Cap 11a, solder joint 15, ribbon 1, solder joint 9, piston rod 8, cap11.

It will be noted that ribbon 1 comprises axially outer or endperforations and axially inner or intermediate perforations. Solderjoint 11 is arranged immediately adjacent to the upper end perforation.The close proximity of solder joint 11 and the upper end perforation isimportant for two reasons. Since all points of reduced cross-section oflink 1 are virtually simultaneously severed on major fault currents,spring 7 has to drag but a short length of link 1 through filler 3 and,therefore,

spring 7 does not need to exert a large force and may be relativelycompact. If link 1 were severed only adjacent its center a large springforce and a large spring would be required to overcome the frictionbetween link 1 and filler 3 or the fulgurite resulting from fusion ofthe latter. Since solder joint 11 is arranged at a point remote fromthat where the highest temperature prevails, the temperatures of solderjoint 11 tend to be relatively low. The proximity of solder joint 11 andthe upper end perforation in link 1 compensates more or less for theofcenter location of solder joint 11.

It will also be understood that a relatively large portion of the totallength of easing 4 is assigned to housing shortcircuit currentinterrupting means, resulting in generation of relatively high arevoltages.

Having disclosed a preferred embodiment of my invention, it is desiredthat the same be not limited to the particular structure disclosed. ItWill be obvious to any person skilled in the art that many modificationsand changes may be made Without departing from the spirit and scope ofmy invention as set forth in the appended claims.

I claim as my invention:

1. An electric dual element fuse comprising in combination:

(a) a single continuous fusible element adapted to fuse only atrelatively high fault currents;

(b) a pulverulent arc-quenching substance embedding said element;

() means for housing said element and said substance, said housing meansincluding a tubular casing of insulating material;

(d) a piston;

(e) a spring biasing said piston;

(f) a pair of terminal caps mounted on the lateral outer surface of saidcasing, one of said pair of caps having an end surface substantiallyflush with one of the ends of said casing and being conductivelyconnected to one end of said fusible element and the other of said pairof caps defining a chamber inside said casing housing said piston andsaid spring and segregating said piston and said spring from saidsubstance, the portion of said other of said pair of caps-deiining saidchamber being arranged immediately adjacent to the other of the ends ofsaid casing;

(g) a conductive piston rod arranged on one side of said piston andprojecting transversely through said other of said pair of caps towardsaid fusible element;

(h) a soft solder joint securing said piston rod to said fusible elementadapted to soften only at relatively small protracted overload currents;and

(i) an external indicator pin arranged on the side of said piston remotefrom said solder joint and jointly movable with said piston upon fusionof said fusible element as Well as upon fusion of said solder joint.

2. An electric dual element fuse comprising in combination:

(a) a fusible element formed by a single multiperforated length ofribbon adapted to fuse only at relatively high fault currents;

(b) a pulverulent arc-quenching substance embedding said ribbon;

(0) means for housing said ribbon and said substance, said housing meansincluding a tubular casing of insulating material projecting beyond saidribbon on one end thereof to provide a tubular space unoccupied by saidribbon;

(at) a piston arranged in said space in coaxial relation to said casing;

(e) a compressed spring arranged in said space biasing said piston awayfrom said ribbon;

(f) a pair of terminal caps mounted on the lateral outer surface of saidcasing, one of said pair of caps having an end surface substantiallyflush with one of the ends of said casing and conductively connected toone end of said ribbon, and the other of said pair of caps defining ahousing inside said casing at said end thereof unoccupied by said ribbonaccommodating said piston and said spring and segregating said pistonand said spring from said substance;

(g) a piston rod having a larger current-carrying capacity than saidribbon arranged on one side of said piston and projecting transverselythrough said other of said pair of caps toward said ribbon;

(h) a soft solder joint securing said piston to the end of said ribbonadjacent said other of said pair of caps and adapted to soften only atrelatively small protracted overload currents; and

(i) an indicator pin arranged on the side of said piston remote fromsaid solder joint and jointly movable with said piston upon fusion ofsaid solder joint as well as upon fusion of said ribbon.

3 An electric dual element fuse comprising in combination:

(a) a tubular casing of insulating material having a predeterminedlength;

([2) a fusible ribbon having a plurality of perforations spaced in adirection longitudinally thereof and including end perforations andintermediate perforations, said ribbons being arranged inside 'saidcasing and having a length shorter than said predetermined length, oneend of said ribbon extending to one end of said casing and the other endof said ribbon being spaced from the other end of said casing;

(c) a pair of terminal caps mounted on the lateral outer surface of saidcasing and closing the ends thereof, one of said pair of caps defining arecess coaxial with said casing and extending into said casing in adirection longitudinally thereof and the other of said pair of capshaving an end surface substantially tiush with one of said ends of saidcasing, said other of said pair of caps being conductively connected toone of the ends of said ribbon;

(d) a piston arranged in said recess;

(2) a compressed helical spring arranged in said recess biasing saidpiston away from the bottom of said recess;

(f) a pin attached to one side of said piston adapted to project beyondsaid casing upon movement of said piston under the bias of said spring;

(g) a piston rod secured to the other side of said piston projectingthrough said one of said pair of caps into said casing, said piston rodhaving a slot extending in a direction longitudinally thereof andengaged by the other end of said ribbon; and

(h) a solder join-t substantially coextensive with said slotconductively connecting said piston rod to said other end of saidribbon, and said solder joint being 5 arranged immediately adjacent toone of said end perforations of said ribbon.

4. A dual element fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pair of terminal caps mounted upon the lateral outer surface ofsaid casing and closing said casing, one of said pair of caps defining arecess coaxial with said casing and extending into said casing and theother of said pair of caps having an end surface substantially flushwith one end of said casing;

(c) a multiperforated ribbon fuse link having one end immediatelyadjacent to the end surface of said one of said pair of caps andconductively connected to said one of said pair of caps and said fuselink having another end spaced from one of the ends of said casing;

(d) a pulverulent arc-quenching filler inside said casing embedding saidribbon fuse link;

(e) a piston inside said recess including a piston rod integral withsaid piston having one end projecting through said one of said pair ofterminal caps into said casing, said piston rod having a slot extending6 in a direction longitudinally thereof engaged by said another end ofsaid fuse link;

(f) a mass of solder inside said slot conductively connecting said endof said piston rod to said another end of said ribbon fuse link; and

(g) spring means biasing said piston to cause movement of said pistonrelative to said casing both in response to fusion of said mass ofsolder and in response to fusion of said ribbon fuse link atperforations thereof.

References Cited by the Examiner UN TED STATES PATENTS 2,026,381 12/35Fiedler 200121 2,321,711 6/43 Taylor 200-123 FOREIGN PATENTS 180,8246/22 Great Britain.

542,667 5/56 Belgium.

BERNARD A. GILHEANY, Primary Examiner.

1. AN ELECTRIC DUAL ELEMENT FUSE COMPRISING IN COMBINATION: (A) A SINGLECONTINUOUS FUSIBLE ELEMENT ADAPTED TO FUSE ONLY AT RELATIVELY HIGH FAULTCURRENTS; (B) A PULVERULENT ARC-QUENCHING SUBSTANCE EMBEDDING SAIDELEMENT; (C) MEANS FOR HOUSING SAID ELEMENT AND SAID SUBSTANCE, SAIDHOUSING MEANS INCLUDING A TUBULAR CASING OF INSULATING MATERIAL; (D) APISTON; (E) A SPRING BIASING SAID PISTON; (F) A PAIR OF TERMINAL CAPSMOUNTED ON THE LATERAL OUTER SURFACE OF SAID CASING, ONE OF SAID PAIR OFCAPS HAVING AN END SURFACE SUBSTANTIALLY FLUSH WITH ONE OF THE ENDS OFSAID CASING AND BEING CONDUCTIVELY CONNECTED TO ONE END OF SAID FUSIBLEELEMENT AND THE OTHER OF SAID PAIR OF CAPS DEFINING A CHAMBER INSIDESAID CASING HOUSING SAID PISTON AND SAID SPRING AND SEGREGATING SAIDPISTON AND SAID SPRING FROM SAID SUBSTANCE, THE PORTION OF SAID OTHER OFSAID PAIR OF CAPS-DEFINING SAID CHAMBER BEING ARRANGED IMMEDIATELYADJACENT TO THE OTHER OF THE ENDS OF SAID CASING; (G) A CONDUCTIVEPISTON ROD ARRANGED ON ONE SIDE OF SAID PISTON AND PROJECTINGTRANSVERSELY THROUGH SAID OTHER OF SAID PAIR OF CAPS TOWARD SAID FUSIBLEELEMENT; (H) A SOFT PAIR OF CAPS TOWARD SAID FUSIBLE ELEMENT; FUSIBLEELEMENT ADAPTED TO SOFTEN ONLY AT RELATIVELY SMALL PROTRACTED OVERLOADCURRENTS; AND (I) AN EXTERNAL INDICATOR PIN ARRANGED ON THE SIDE OF SAIDPISTON REMOTE FROM SAID SOLDER JOINT AND JOINTLY MOVABLE WITH SAIDPISTON UPON FUSION OF SAID FUSIBLE ELEMENT AS WELL AS UPON FUSION OFSAID SOLDER JOINT.